The molecular properties of the apoA-I and apoA-II proteins of human serum high density lipoprotein are being evaluated. The interactions of these two proteins with the phospholipid, lysolecithin, are being evaluated in order to obtain the affinity constants and structural changes in the proteins produced by the phospholipid. The binding of ANS to the gonadotropic hormone from pituitary and chorionic fluid has been studied. The binding exhibits negative cooperativity to the pituitary hormone since only one mole of ANS is bound to two moles of the hormone. Positive cooperativity is observed with the chorionic hormone since four ANS molecules are bound to two moles of the hormone.